This disclosure relates to actuating downhole devices in a wellbore and, more particularly, actuating downhole devices over a wireline by a tonal signal.
Downhole tools and devices utilized in a wellbore may accomplish a number of different tasks. For example, some downhole tools are used for perforating the wellbore to allow fluids from the geological formation to enter the wellbore and eventually be produced. Downhole tools may also be utilized to measure various characteristics of the geological formation surrounding the wellbore; introduce cement, sand, acids, or other chemicals to the wellbore; and perform other operations.
In certain instances, downhole tools, such as explosive perforating tools, or “guns,” utilize a combination of changing voltage polarity and pressure actuated switches in order to activate. For example, a downhole tool may consist of a string of guns physically and electrically connected by a wireline in the wellbore and positioned vertically in the wellbore at a particular depth. In order to activate the first gun in the string, i.e., the deepest gun in the string, a positive voltage signal may be transmitted via the wireline to the first gun, actuating the gun and causing the explosive charge to detonate. A pressure-actuated mechanical switching switch may then shift to allow negative polarity only through the wireline. The second gun in the string, i.e., the next deepest gun in the string, may only be actuated with negative polarity. Once the second gun is actuated by transmitting negative polarity through the wireline, the pressure-actuated mechanical switching switch may shift to allow only positive polarity voltage through the wireline. The third gun in the string may only be actuated with positive voltage. The foregoing sequence of positive and negative voltage actuated tools may be repeated for any number of tools. The pressure actuated mechanical switching switch, however, may be shifted accidentally due to formation characteristics. Moreover, guns actuated by switching polarity may be prone to accidental actuation.